Procedure and apparatus for the weighing of a load

ABSTRACT

The invention concerns a procedure for the weighing of a load. In this procedure a load support having supporters (23), e.g. a vehicle or container, is provided with transducers (1a, 1b, 2) whose output signals are used to determine the weight of the load (K). According to the invention, the transducers are mounted on the rigid frame (4) of the load support near the fixing points (6; 6a, 6b, 6c, 6d) of the supporters (23; 27) and used to measure the deformations and/or stresses caused by the load, the weight of the load being determined on the basis of these.

The present invention relates to a procedure for weighing a load asdefined in the introductory part of claim 1 and to an apparatus forweighing a load as defined in the introductory part of claim 2.

Previously known load-weighing methods use strain gauge transducers inthe weighing of vehicles, especially lorries and their loads. Systemsand equipment of this kind are presented e.g. in the following patentpublications: GB-1366084, GB-1559596, GB-2122748, GB-2178178, U.S. Pat.Nos. 3443652, 3780817, 3800895, 3978908, 3889765 and 4673047.

However, the procedures and equipment proposed in these publicationshave certain drawbacks. They are complex and expensive and verydifficult to install on vehicles already in use as the transducers areplaced on the axle and suspension assemblies. Due to this placement ofthe transducers, these weighing equipments are very susceptible todamage.

The object of the present invention is to eliminate the drawbacksmentioned. A specific object of the invention is to present a new typeof load-weighing procedure and apparatus which is applicable for themeasurement of the weights of the loads of stationary and/or movablevehicles, transport containers and equivalent resting on supporters, andof load supports in general, in such manner that the weighing system iseasy and economical to install even on vehicles or corresponding loadsupports already in use.

The procedure of the invention is characterized by what is presented inclaim 1.

The apparatus of the invention is characterized by what is presented inclaim 2.

In the procedure of the invention, a load support such as a vehicle orcontainer having supporters such as legs or wheels is provided withtransducers and the weight of the load is determined from the signalsgiven by the transducers. According to the invention, the transducersare mounted on the rigid frame of the load support near the fixingpoints of the supporters, and they are used to measure the deformationsand/or stresses caused by the load, the weight of the load beingdetermined on the basis of these.

In a preferred embodiment of the procedure, a vehicle is provided withtransducers and the weight of the load is determined from the signalsgiven by the transducers. According to the invention, the transducersare mounted on the rigid frame of the vehicle, near the fulcrum pointsbetween the axles and the frame, and they are used to measure thedeformations and/or stresses caused by the load, the weight of the loadbeing determined on the basis of these.

The apparatus of the invention for the weighing of a load, which isplaced on a load support provided with supporters, comprises at leastone transducer attached to the load support, and a processing unit forprocessing the signals obtained from the transducers so as to enable theweight of the load to be detected. According to the invention, thetransducers are mounted on the rigid frame of the load support,especially in the immediate vicinity of the fixing points of thesupporters, said transducers measuring the deformations and/or stressesproduced in the frame by the load.

A preferred embodiment of the apparatus comprises at least onetransducer attached to a vehicle, and a processing unit for processingthe signals obtained from the transducers so as to enable the weight ofthe load to be indicated. In this preferred embodiment of the invention,the transducers are mounted on the frame of the vehicle, specifically inthe immediate vicinity of the fixing points of the axle assemblies, saidtransducers measuring the deformations and/or stresses produced in theframe by the load.

In an embodiment of the apparatus, the transducers are preferablymounted on the frame girders of the load support, e.g. a lorry.

In an embodiment of the apparatus, at least two transducers are mountedin the vicinity of each fixing point, e.g. point of suspension.

In an embodiment of the apparatus, the transducers are placed around thefulcrum of a joint turnable in the frame of a trailer.

In an embodiment of the apparatus, the transducers are attached tightly,e.g. by glueing, to the measuring points.

In an embodiment of the apparatus, it is provided with means fortemperature compensation of the transducers.

In an embodiment of the apparatus, the transducers are strain gauges.

In an embodiment of the apparatus, the transducers are optoelectrictransducers.

In an embodiment of the apparatus, the transducers are piezoelectrictransducers.

The essential point in the procedure and apparatus of the invention isthat the transducers are placed on rigid, fixed and strong parts of theload support, in positions suitably protected. The transducers arepreferably placed above the fixing points of the supporters in such away that they can measure small deformations of the load support framecaused by the load and its variations.

As compared to previously known techniques, the procedure and apparatusof the invention have the advantage that the transducers and the wholeapparatus can be easily and quickly installed on lorries, containers andequivalent load supports, whether new or already in use. Mounted on theframe girders of a lorry or an equivalent load support, the transducersare not so exposed to impacts and wear as the transducers used incurrent equipment, and the simplicity of installation of the apparatusallows it to be installed on any vehicle regardless of model and size.

In the following, the invention is described in detail by referring tothe appended drawing, in which:

FIG. 1 presents a diagrammatic lateral view of a transducer arrangementof the apparatus of the invention as mounted on the frame of a lorry,

FIG. 2 presents a graphic top-view illustration of a trailer attachableto a traction vehicle, with the upper structures of the trailer frameremoved, the transducer arrangement of the apparatus of the inventionbeing installed on the trailer frame,

FIG. 3a presents an arrangement for the attachment of a strain gauge toa rigid frame girder of a lorry or equivalent,

FIG. 3b presents a similar arrangement for the attachment of two straingauges,

FIG. 4 presents the circuit diagram of an apparatus of the invention,

FIG. 5 presents the circuit diagram of another apparatus of theinvention, and

FIG. 6 presents a diagrammatic lateral view of the transducerarrangement of an apparatus of the invention as mounted on a containerstanding on supporters.

FIG. 1 shows a transducer arrangement of the apparatus of the inventionas mounted on the frame of a vehicle, e.g. a lorry. The axle assembly 5and springs 11 of the vehicle are suspended on the frame girders 7 ofthe lorry only by the supporting points 6; 6a, 6b; 6c, 6d. Therefore,the stresses caused by the weight of vehicle frame 4 and the wholevehicle and its load K are applied to these supporting points 6 andthrough these and the axle assembly 5 and wheels 23 (indicated withbroken lines) to the ground.

According to the invention, the frame girder 7 is provided withtransducers 1; 1a, 1b and 2, e.g. strain gauges, mounted in theimmediate vicinity of the supporting points 6. The transducers are usedto measure the stresses applied to the frame 7 from the deformationscaused by them. There may be one or more transducers 1, 2 around one andthe same supporting point 6. They are connected to a common processingunit to give a measurement signal proportional to the load.

The transducers 1; 1a, 1b; 2 are placed above the supporting points 6;6a, 6b; 6c, 6d, or more generally above the straight line A--Aconnecting the supporting points 6; 6a, 6b; 6c, 6d. In this way, thedeformation, especially elongation, can be measured. The magnitude ofthe deformation depends on the magnitude of the load.

The rear axle assemblies 5a, 5b of the trailer in the embodiment of theinvention illustrated in FIG. 2 are suspended on the frame 4 in a mannercorresponding to FIG. 1. Two transducers 1a, 1b are mounted on the framegirders 7 near each supporting point 6a, 6b; 6c, 6d of each axleassembly 5a, 5b. The front axle 12 is turnably mounted on a supportingplate 14 by means of a joint 10 at the fulcrum point B. The supportingplate 14 is attached to the frame 4, e.g. frame girders 7, by means ofbrackets 9. Four transducers 3; 3a, 3b, 3c and 3d are placedsymmetrically around the fulcrum or supporting point B of the joint, onepair of transducers 3a, 3b being placed on the right-hand side of theframe 4 relative to the fulcrum point B and another pair 3c, 3d on theleft-hand side. The transducers 3 are used to measure the deformationsof the supporting plate 14 when the trailer 30 is standing still, thestresses caused by the weight being measured from the deformations.

FIG. 3a illustrates the manner in which a strain gauge 2 is mounted on aframe girder 7 of a vehicle, a trailer or an equivalent load support.The strain gauge 2 is attached tightly, e.g. by glueing, to the upperedge of the frame girder 7 above the supporting point 6. In addition,the strain gauge 2 is fitted at a suitable location in the longitudinaldirection A--A of the girder so that the small elongation produced bythe load K in the frame girder in the region above the supporting point6 is transmitted to the gauge and a measurement signal is obtained fromit.

FIG. 3b shows how two strain gauges 2; 2a, 2b are mounted on a framegirder 7 corresponding to that in FIG. 3a. In this case, the straingauges 2; 2a, 2b are attached in a crosswise manner to the upper edge ofthe girder 7 above the supporting point 6. Relative to the longitudinaldirection of the girder 7, the strain gauges 2a, 2b are placed at anangle, preferably 45° and 135°, and at straight angles relative to eachother. Electrically, the gauges are connected together in series andalso to a suitable processing unit.

In the embodiment illustrated by FIG. 2, the transducers 1, 3 on eachaxle assembly 5a, 5b, 12 are connected in series and connected to aprocessing unit 8 according to the circuit diagram shown in FIG. 4, aseparate processing unit 8 being provided for each axle assembly. Bycalibrating the equipment in a suitable manner, the loads imposed oneach axle assembly can be measured separately. By combining these datae.g. by means of a microprocessor-based data processing apparatus, thetotal load and weight of the vehicle, among other things, areestablished.

FIG. 4 shows the circuit diagram of an apparatus according to theinvention. The processing unit, 8 comprises a measuring circuitconsisting of a measuring bridge made up of series-connected transducers15 (e.g. transducers 6a, 6b, 6c and 6d on axle assembly 5a in FIG. 2), avariable resistor 16, two compensating resistors 17 and a d.c. source 18connected across the bridge. By means of the variable resistor 17, themeasuring bridge can be calibrated after installation as required foreach vehicle. The d.c. signal obtained from the measuring bridge,representing the axle load of the vehicle being weighed, is summed andamplified by an amplifier 19, from where the signal is passed into aprocessing and controller unit 20. In this unit, the signal is convertedinto digital form by means of an A/D converter, processed and fed e.g.into a display 21. The measurement signal can also be output from theprocessing unit into a suitable data processing unit and/or stored inmemory, from where it can easily be retrieved when necessary, e.g. alongwith other data relating to the load, such as the other axle loads ofthe vehicle.

In the apparatus of the invention, the transducers 1, 2, 3 arepreferably temperature-compensated as the outside temperature variesconsiderably with the times of the year e.g. in Northern Europe. Withoutautomatic compensation, the measurement results obtained from thetransducers would vary significantly with temperature, or the apparatuswould have to be calibrated each time the weather changes.

The temperature compensation is advantageously realized by means of atemperature transducer 22 (FIG. 3a), which is e.g. a resistor whoseresistance varies with temperature. The temperature transducer 22 isconnected to the processing unit 8, e.g. to the variable resistor 16 inthe measuring bridge to vary its resistance in accordance with thechanges in temperature.

FIG. 5 shows the circuit diagram of another apparatus of the invention.The processing unit 8a comprises a measuring circuit consisting of twotransducers 1a, 1b, preferably optoelectric transducers, an amplifier24, and a d.c. source 18 connected across the transducers and theamplifier. The optic transducer comprises a light source and a detectorwhose output signal represents the weight of the load under measurement.The signals obtained from the two transducers are fed into the amplifier24, where they are summed and amplified. The amplified signal is thenpassed into a processing and controller unit 20. In this unit, thesignal is converted into digital form by means of an A/D converter,processed and fed e.g. into a display 21. The optic transducers 1a, 1bare placed in the vicinity of the supporting points 6 of the vehicle orequivalent as shown e.g. in FIG. 1.

FIG. 6 presents a container 28 or an equivalent load support which cancarry a load inside or upon it. The container 28 is supported bysupporters 27. The rigid frame 25 of the container, specifically one ofits rigid bottom girders 25a, is provided with a transducer arrangementaccording to the invention. The transducers 1a, 1b are mounted near thefixing points 26 of the supporters 27 in a manner corresponding to theembodiment in FIG. 1. This embodiment, too, may have one or moretransducers 1a, 1b, 2 placed around one and the same fixing point andconnected to a common processing unit to give a measurement signalproportional to the stress present at the fixing point and especially tothe load K of the container.

In the embodiments described above, the transducers are strain gauges oroptoelectic transducers. Other types of transducers measuring stressand/or deformation may also be used.

In an embodiment of the apparatus, piezoelectric transducers are used.The operation of this type of transducer is based on the piezoelectriceffect. The transducer is a crystal made of a piezoelectric materialsuch as quartz. Mechanical stress applied to the crystal generates asmall potential difference between the ends of the crystal. Apiezoelectric transducer is firmly attached e.g. to a frame girder of avehicle in the manner presented e.g. in FIG. 3a. In this case, thetransducer must be isolated from the frame girder. The potentialdifference across the transducer, which is proportional to the load K,is measured e.g. by means of a circuit arrangement as shown in FIG. 5.

In the foregoing, the invention has been described by referring to someof its preferred structural solutions, yet different embodiments arepossible within the scope of the idea of the invention as defined in thefollowing claims.

I claim:
 1. A method for weighing a load in a vehicle such as a truck, atrailer or the like, in which method at least one strain gauge ismounted on a rigid frame, such as a frame girder, of the vehicle,wherein the strain gauge is used to measure deformation and stress ofthe rigid frame caused by the load, a weight of the load beingdetermined on a basis of the measured deformation and stress, the methodcomprising the steps of:mounting the strain gauge on the rigid frame,such as the frame girder, in a vicinity of a supporting point of an axleassembly in the frame girder; mounting a second strain gauge in thevicinity of the supporting point, so that at least two strain gauges areplaced in the vicinity of each supporting point; applying the load onthe truck; and measuring the deformation and stress of the rigid frameby the strain gauges.
 2. An apparatus used for weighing a load in avehicle such as a truck, a trailer or the like, the apparatuscomprising:at least one strain gauge being attached to a rigid frame,such as a frame girder, of the vehicle, the strain gauge being arrangedto measure deformation and stress produced in the rigid frame by theload; processing means, connected to the strain gauge, for processing asignal obtained from the strain gauge to indicate a weight of the load;the strain gauge being attached to the rigid frame, such as the framegirder in the vicinity of a supporting point of an axle assembly in theframe girder; and a second strain gauge being attached to the rigidframe in the vicinity of the supporting point, so that at least twostrain gauges are placed in the vicinity of each supporting point.
 3. Anapparatus according to claim 2, wherein the strain gauges are attachedtightly, such as by gluing, to a measuring point.
 4. An apparatusaccording to claim 2, further comprising means for compensatingtemperature of the strain gauges.
 5. An apparatus according to claim 3,further comprising means for compensating temperature of the straingauges.